A typical film-type camera includes a mechanical shutter. Light is reflected off of a scene from either artificial or natural light conditions. The camera receives the reflected light when the mechanical shutter is opened. While the shutter is opened, the reflected light is focused on a film that contains light sensitive components. The light sensitive components of the film create a chemical recording of the received light. The image, or scene, that is recorded on the film corresponds to the total amount of light that directed onto the film during exposure to the reflected light. The total amount of light directed onto the film is related to the aperture of the shutter, and the exposure time. The exposure time of the film corresponds to the length of time that the mechanical shutter is open. The exposure time is a fixed time interval that is manually adjusted by an operator.
Digital cameras are similar to film-type cameras in that light is reflected off of the scene and received by a light sensitive component when the shutter is open. The light sensitive component may be a charge coupled device (CCD), or a complementary metal oxide semiconductor (CMOS) device. The image sensors convert light into electronic signals when exposed. The signals are provided to an image processor to store the image of the recorded scene. In digital cameras, the shutter may be a mechanical shutter that is similar to that found in the film-type camera, or an electronic shutter mechanism.
A typical image sensor includes an array of image capturing points, or pixels. Each pixel is arranged to provide a signal that is responsive to light. The signal level that is provided by each pixel is related to the intensity of the light that is received, and the length of time that the pixel is exposed. A CMOS array is arranged in rows and columns that may be read individually, while a CCD array typically provides a serial read out of the electronic signals. The electronic signals are typically converted into digital signals that are stored in a memory circuit, such that the digitized image is captured.